Fix inconsistent naming of pcalls between docs and code.

In the docs of Stats.sort_stats pcalls is named primitive call count.
In the code at Stats.sort_arg_dict_default it was just named call count.

Adjusted Stats.sort_arg_dict_default to name pcalls primitive call count, too.

diff -r 822d7a1f8885 -r 127eda0b7610 Lib/pstats.py
--- a/Lib/pstats.py	Tue Jan 31 02:55:32 2012 -0500
+++ b/Lib/pstats.py	Thu May 24 11:20:21 2012 +0200
@@ -178,7 +178,7 @@
               "module"    : (((4, 1),              ), "file name"),
               "name"      : (((6, 1),              ), "function name"),
               "nfl"       : (((6, 1),(4, 1),(5, 1),), "name/file/line"),
-              "pcalls"    : (((0,-1),              ), "call count"),
+              "pcalls"    : (((0,-1),              ), "primitive call count"),
               "stdname"   : (((7, 1),              ), "standard name"),
               "time"      : (((2,-1),              ), "internal time"),
               }